Extension of the depth of focus of imaging is a common goal of various imaging systems. Techniques for extending the depth of focus of imaging systems have been developed, and are described for example in the following publications:
U.S. Pat. No. 6,536,898 and U.S. Pat. No. 7,025,454 disclose extended depth of field optics for human eye. This technique utilizes modification of contact lenses, intraocular implants, and/or the surface of the eye itself. This is accomplished by applying selected phase variations to these optical elements (e.g., by varying surface thickness of the cornea of the eye). The phase variations EDF-code the wavefront and cause the optical transfer function to remain essentially constant within a range of distances from the in-focus position. This provides a coded image on the retina. The human brain decodes this coded image, resulting in an in-focus image over an increased depth of field.
US 2009/0279189 describes a lens having extended depth of focus. The lens includes a plurality of lens layers, each lens layer being axi-symmetric and having an extended depth of focus to focus light in a corresponding section of a focal curve in the form of a straight line located on an optical axis. In the optical system, light is focused on an optical axis to obtain a clear image in a wide distance range between a camera and an object. The optical system has a point spread function that is simpler and more symmetric. That is, the optical system provides improved continuity of a lens surface and easiness and flexibility in optical designing.
U.S. Pat. Nos. 7,365,917, 7,061,693, WO 07/141788, all assigned to the assignee of the present application, describe all-optical techniques for extending the depth of focus being thus suitable for use in ophthalmic applications. According to these techniques, an imaging arrangement comprises an imaging lens having a certain affective aperture, and an optical element associated with said imaging lens. The optical element is configured as a phase-affecting, substantially non-diffractive optical element defining a spatially low frequency phase transition. The optical element and the imaging lens define a predetermined pattern formed by spaced-apart substantially optically transparent features of different optical properties.